共查询到20条相似文献,搜索用时 15 毫秒
1.
The prediction that environmental fluctuations may destabilise populations and yet stabilise aggregate community properties has remained largely untested. We examined population and community stability under constant and fluctuating temperatures in simple planktonic assemblages of differing algal richness. Temperature dependent resource competition produced a highly asymmetric community structure where algal community biomass was dominated by one species. For a given level of species richness, temperature fluctuations induced lower community covariance and thus stabilised community biomass. However, increasing algal species richness increased the variability of population abundance and growth rates, as well as population and community variability. Consumer dynamics were directly destabilised by environmental fluctuations. These results confirm recent theoretical studies suggesting a stabilising effect of environmental fluctuations at the community level. However, they also support the theoretical prediction that increasing species richness may be of limited value for community stability, most especially in asymmetric communities, when competition directly affects population variability. 相似文献
2.
Density Effects on the Size Structure of Annual Plant Populations: An Indication of Neighbourhood Competition 总被引:4,自引:0,他引:4
Size variability among plants has been observed to increasewith higher stand density, leading to the speculation that resourcedistribution among competing plants is primarily asymmetricrather than symmetric. The relationships between size variability,stand density, and type of resource distribution among competingplants were investigated using a spatially explicit, individual-plantmodel of annual plant population dynamics. When plants variedin neighbourhood competition, size variability increased withhigher stand densities whether shared resources were symmetricallyor asymmetrically distributed among competing plants. Size variabilitydid not increase with higher stand densities when neighbourhoodcompetition was constant for all plants. These simulations indicatethat increased size variability among competing plants doesnot distinguish between symmetric and asymmetric resource distribution,but rather is direct evidence for neighbourhood competition. Size hierarchy, neighbourhood competition, density effects, asymmetric competition, symmetric competition 相似文献
3.
D. Brian Walton Benjamin P. Leard Anthony Tongen 《Bulletin of mathematical biology》2010,72(5):1092-1123
We consider a model for a population in discrete time with nonoverlapping generations that has fecundity proportional to the
amounts of two essential resources obtained up to a saturating level. A population’s strategy defines how individuals divide
their total available energy between efforts to obtain the two resources. We assume that the total amount of each resource
obtained is a positive, increasing, concave down function of the total energy exerted toward the resource. By considering
two competing subpopulations that have different energy allocation strategies, we characterize the stability of all possible
equilibria and find a unique optimal strategy where a fixed subpopulation resists invasion by a small competing subpopulation
using any other strategy. Except when one of the resources is readily obtained above the saturation level, this optimal strategy
is to divide effort equally between the resources. We illustrate the behavior of the model, directly showing the effects of
an invading subpopulation with pairwise invasibility plots. 相似文献
4.
Many animal species live in groups. Group living may increase exploitation competition within the group, and variation among groups in intra-group competition intensity could induce life-history variability among groups. Models of physiologically structured populations generally predict single generation cycles, driven by exploitation competition within and between generations. We expect that life-history variability and habitat heterogeneity induced by group living may affect such competition-driven population dynamics. In this study, we vary the gregariousness (the tendency to aggregate in groups) of a size-structured consumer population in a spatially explicit environment. The consumer has limited mobility, and moves according to a probabilistic movement process. We study the effects on the population dynamics, as mediated through the resource and the life-history of the consumer. We find that high gregariousness leads to large spatial resource variation, and highly variable individual life-history, resulting in highly stochastic population dynamics. At reduced gregariousness, life-history of consumers synchronizes, habitat heterogeneity is reduced, and single generation cycles appear. We expect this pattern to occur for any group living organism with limited mobility. Our results indicate that constraints set by population dynamical feedback may be an important aspect in understanding group living in nature. 相似文献
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6.
Organisms are often observed to acquire an excess of non-limiting resources, a process known as luxury consumption. Luxury
consumption has been largely treated as a bet hedging strategy for temporal variation in resource supply, but may also function
as a competitive strategy. We incorporate luxury resource consumption into a derivation of the classic resource ratio model
for competition between terrestrial plant, and explore its consequences for population dynamics and competition. We show that
luxury consumption reduces the potential for coexistence between two species competing for two resources. Furthermore, we
demonstrate that luxury consumption can be selected for because of the competitive advantage that luxury consumers gain. Luxury
consumption evolves when competition for resources is local rather than global, there is potential for coexistence between
the two species and the competitive environment remains stable over a sufficient period of time to allow selection to act.
The evolutionary outcome can be either extinction of one of the competing species or coexistence of the two species with maximum
luxury consumption. The potential for selection to favor luxury consumption is well predicted by the competitive outcome between
individuals of the two species with and without luxury consumption. 相似文献
7.
Doanh Nguyen Ngoc Rafael Bravo de la Parra Miguel A. Zavala Pierre Auger 《Journal of theoretical biology》2010,266(2):256-263
We investigate whether asymmetric fast migration can modify the predictions of classical competition theory and, in particular revert species dominance. We consider a model of two species competing for an implicit resource on a habitat divided into two patches. Both patches are connected through constant migration rates and in each patch local dynamics are driven by a Lotka-Volterra competition system.Local competition is asymmetric with the same superior competitor in both patches. Migration is asymmetric, species dependent and fast in comparison to local competitive interactions. The species and patches are taken to be otherwise similar: in both patches we assume the same carrying capacities for both species, and the same growth rates and pair-wise competition coefficients for each species.We show that global dynamics can be described by a classical Lotka-Volterra competition model. We found that by modifying the ratio of intraspecific migration rates for both species all possible combinations of global species relative dominance can be achieved. We find specific conditions for which the local superior competitor is globally excluded. This is to our knowledge the first study showing that fast asymmetric migration can lead to inferior competitor dominance in a homogeneous environment. We conclude that disparity of temporal scales between migration and local dynamics may have important consequences for the maintenance of biodiversity in spatially structured populations. 相似文献
8.
Stomp M van Dijk MA van Overzee HM Wortel MT Sigon CA Egas M Hoogveld H Gons HJ Huisman J 《The American naturalist》2008,172(5):169-185
Although phenotypic plasticity can be advantageous in fluctuating environments, it may come too late if the environment changes fast. Complementary chromatic adaptation is a colorful form of phenotypic plasticity, where cyanobacteria tune their pigmentation to the prevailing light spectrum. Here, we study the timescale of chromatic adaptation and its impact on competition among phytoplankton species exposed to fluctuating light colors. We parameterized a resource competition model using monoculture experiments with green and red picocyanobacteria and the cyanobacterium Pseudanabaena, which can change its color within approximately 7 days by chromatic adaptation. The model predictions were tested in competition experiments, where the incident light color switched between red and green at different frequencies (slow, intermediate, and fast). Pseudanabaena (the flexible phenotype) competitively excluded the green and red picocyanobacteria in all competition experiments. Strikingly, the rate of competitive exclusion was much faster when the flexible phenotype had sufficient time to fully adjust its pigmentation. Thus, the flexible phenotype benefited from its phenotypic plasticity if fluctuations in light color were relatively slow, corresponding to slow mixing processes or infrequent storms in their natural habitat. This shows that the timescale of phenotypic plasticity plays a key role during species interactions in fluctuating environments. 相似文献
9.
The consequences of within-cohort (i.e., among-individual) variation for population dynamics are poorly understood, in particular for the case where life history is density dependent. We develop a physiologically structured population model that incorporates individual variation among and within cohorts and allows us to explore the intertwined relationship between individual life history and population dynamics. Our model is parameterized for the lizard Zootoca vivipara and reproduces well the species' dynamics and life history. We explore two common mechanisms that generate within-cohort variation: variability in food intake and variability in birth date. Predicted population dynamics are inherently very stable and do not qualitatively change when either of these sources of individual variation is introduced. However, increased within-cohort variation in food intake leads to changes in morphology, with longer but skinnier individuals, even though mean food intake does not change. Morphological changes result from a seemingly universal nonlinear relationship between growth and resource availability but may become apparent only in environments with strongly fluctuating resources. Overall, our results highlight the importance of using a mechanistic framework to gain insights into how different sources of intraspecific variability translate into life-history and population-dynamic changes. 相似文献
10.
Stephen R. Proulx Snigdhadip Dey Thiago Guzella Henrique Teotnio 《Ecology letters》2019,22(11):1767-1775
Different modes of non‐genetic inheritance are expected to affect population persistence in fluctuating environments. We here analyse Caenorhabditis elegans density‐independent per capita growth rate time series on 36 populations experiencing six controlled sequences of challenging oxygen level fluctuations across 60 generations, and parameterise competing models of non‐genetic inheritance in order to explain observed dynamics. Our analysis shows that phenotypic plasticity and anticipatory maternal effects are sufficient to explain growth rate dynamics, but that a carryover model where ‘epigenetic’ memory is imperfectly transmitted and might be reset at each generation is a better fit to the data. We further find that this epigenetic memory is asymmetric since it is kept for longer when populations are exposed to the more challenging environment. Our analysis suggests that population persistence in fluctuating environments depends on the non‐genetic inheritance of phenotypes whose expression is regulated across multiple generations. 相似文献
11.
Demographic heterogeneity influences how populations respond to density dependent intraspecific competition and trophic interactions. Distinct stages across an organism's development, or ontogeny, are an important example of demographic heterogeneity. In consumer populations, ontogenetic stage structure has been shown to produce categorical differences in population dynamics, community dynamics and even species coexistence compared to models lacking explicit ontogeny. The study of consumer–resource interactions must also consider the ontogenetic stage structure of the resource itself, particularly plants, given their fundamental role at the basis of terrestrial food webs. We incorporate distinct ontogenetic stages of plants into an adaptable multi-stage consumer–resource modeling framework that facilitates studying how stage specific consumers shape trophic dynamics at low trophic levels. We describe the role of density dependent demographic rates in mediating the dynamics of stage-structured plant populations. We then investigate how these demographic rates interact with consumer pressure to influence stability and coexistence in multiple stage-specific consumer–resource interactions. Results detail how density dependent effects across distinct ontogenetic stages in plant development produce non-additivity in the drivers of dynamic stability both in single populations and in consumer–resource settings, challenging the ubiquity of certain traditional ecological dynamic paradigms. We also find categorical differences in the population variability induced by herbivores consuming separate plant stages. Consumer–resource models, such as plant–herbivore interactions, often average out demographic heterogeneity in populations. Here, we show that explicitly including plant demographic heterogeneity through ontogeny yields distinct dynamic expectations for both plants and herbivores compared to traditional consumer–resource formulations. Our results indicate that efforts to understand the demographic effect of herbivores on plant populations may need to also consider the effects of plant demographics on herbivores and the reciprocal relationship between them. 相似文献
12.
KEVIN L. KIRK 《Freshwater Biology》2002,47(6):1089-1096
1. In a constant environment, competition often tends to reduce species diversity. However, several theories predict that temporal variation in the environment can slow competitive exclusion and allow competing species to coexist. This study reports on laboratory competition experiments in which two pairs of planktonic rotifer species competed for a phytoplankton resource under different conditions of temporal variability in resource supply.
2. For both species pairs, Keratella cochlearis dominated under all conditions of temporal variability, and the other species ( Brachionus calyciflorus or Synchaeta sp.) almost always went extinct. Increasing temporal variation in resource supply slowed competitive exclusion but did not change competitive outcome or allow coexistence.
3. Rotifers show a gleaner–opportunist trade-off, because gleaner species have low threshold resource levels ( R *) and low maximum population growth rates, while opportunist species have the opposite characteristics. In the competition experiments, the gleaner always won and the opportunists always lost. Thus, a gleaner–opportunist trade-off was not sufficient to facilitate coexistence under conditions of resource variability. Instead, the winning species had both the lowest R * and the greatest ability to store resources and ration their use during times of extreme resource scarcity. 相似文献
2. For both species pairs, Keratella cochlearis dominated under all conditions of temporal variability, and the other species ( Brachionus calyciflorus or Synchaeta sp.) almost always went extinct. Increasing temporal variation in resource supply slowed competitive exclusion but did not change competitive outcome or allow coexistence.
3. Rotifers show a gleaner–opportunist trade-off, because gleaner species have low threshold resource levels ( R *) and low maximum population growth rates, while opportunist species have the opposite characteristics. In the competition experiments, the gleaner always won and the opportunists always lost. Thus, a gleaner–opportunist trade-off was not sufficient to facilitate coexistence under conditions of resource variability. Instead, the winning species had both the lowest R * and the greatest ability to store resources and ration their use during times of extreme resource scarcity. 相似文献
13.
We investigate conditions under which a model with stochastic demography or population structure converges to the coalescent with a linear change in timescale. We argue that this is a necessary condition for the existence of a meaningful effective population size. We find that such a linear timescale change is obtained when demographic fluctuations and coalescence events occur on different timescales. Simple models of population structure and randomly fluctuating population size are used to exemplify the ideas and provide an intuitive feel for the meaning of the conditions. 相似文献
14.
Optimal life histories in a fluctuating environment are likely to differ from those that are optimal in a constant environment,
but we have little understanding of the consequences of bounded fluctuations versus episodic massive mortality events. Catastrophic
disturbances, such as floods, droughts, landslides and fires, substantially alter the population dynamics of affected populations,
but little has been done to investigate how catastrophes may act as a selective agent for life-history traits. We use an individual-based
model of population dynamics of the stream-dwelling salmonid marble trout (Salmo marmoratus) to investigate how trade-offs between the growth and mortality of individuals and density-dependent body growth can lead
to the maintenance of a wide or narrow range of individual variation in body growth rates in environments that are constant
(i.e., only demographic stochasticity), variable (i.e., environmental stochasticity), or variable with catastrophic events
that cause massive mortalities (e.g., flash floods). We find that occasional episodes of massive mortality can substantially
reduce persistent variability in individual growth rates. Lowering the population density reduces density dependence and allows
for higher fitness of more opportunistic strategies (rapid growth and early maturation) during the recovery period. 相似文献
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16.
We study a two species competition model in which the species have the same population dynamics but different dispersal strategies
and show how these dispersal strategies evolve. We introduce a general dispersal strategy which can result in the ideal free
distributions of both competing species at equilibrium and generalize the result of Averill et al. (2011). We further investigate the convergent stability of this ideal free dispersal strategy by varying random dispersal rates,
advection rates, or both of these two parameters simultaneously. For monotone resource functions, our analysis reveals that
among two similar dispersal strategies, selection generally prefers the strategy which is closer to the ideal free dispersal
strategy. For nonmonotone resource functions, our findings suggest that there may exist some dispersal strategies which are
not ideal free, but could be locally evolutionarily stable and/or convergent stable, and allow for the coexistence of more
than one species. 相似文献
17.
We construct a population dynamics model of the competition among immune system cells and generic tumor cells. Then, we apply the theory of optimal control to find the optimal schedule of injection of autologous dendritic cells used as immunotherapeutic agent.The optimization method works for a general ODE system and can be applied to find the optimal schedule in a variety of medical treatments that have been described by a mathematical model. 相似文献
18.
Teppo Hiltunen Jouni Laakso Veijo Kaitala Lotta-Riina Suomalainen Minna Pekkonen 《Acta Oecologica》2008,33(3):291-299
Competition theory generally predicts that diversity is maintained by temporal environmental fluctuations. One of the many suggested mechanisms for maintaining diversity in fluctuating environments is the gleaner-opportunist trade-off, whereby gleaner species have low threshold resource levels and low maximum growth rates in high resource concentration while opportunist species show opposite characteristics. We measured the growth rates of eight heterotrophic aquatic bacteria under different concentrations of chemically complex plant detritus resource. The growth rates revealed gleaner-opportunist trade-offs. The role of environmental variability in maintaining diversity was tested in a 28-day experiment with three different resource fluctuation regimes imposed on two four-species bacterial communities in microcosms. We recorded population densities with serial dilution plating and total biomass as turbidity. Changes in resource availability were measured from filter-sterilised medium by re-introducing the consumer species and recording short-term growth rates. The type of environmental variation had no effect on resource availability, which declined slowly during the experiment and differed in level between the communities. However, the slowly fluctuating environment had the highest Shannon diversity index, biomass, and coefficient of variation of biomass in both communities. We did not find a clear link between the gleaner-opportunist trade-off and diversity in fluctuating environments. Nevertheless, our results do not exclude this explanation and support the general view that temporal environmental variation maintains species diversity also in communities feeding chemically complex resource. 相似文献
19.
Johansson J 《Evolution; international journal of organic evolution》2008,62(2):421-435
The role and importance of ecological interactions for evolutionary responses to environmental changes is to large extent unknown. Here it is shown that interspecific competition may slow down rates of adaptation substantially and fundamentally change patterns of adaptation to long-term environmental changes. In the model investigated here, species compete for resources distributed along an ecological niche space. Environmental change is represented by a slowly moving resource maximum and evolutionary responses of single species are compared with responses of coalitions of two and three competing species. In scenarios with two and three species, species that are favored by increasing resource availability increase in equilibrium population size whereas disfavored species decline in size. Increased competition makes it less favorable for individuals of a disfavored species to occupy a niche close to the maximum and reduces the selection pressure for tracking the moving resource distribution. Individual-based simulations and an analysis using adaptive dynamics show that the combination of weaker selection pressure and reduced population size reduces the evolutionary rate of the disfavored species considerably. If the resource landscape moves stochastically, weak evolutionary responses cause large fluctuations in population size and thereby large extinction risk for competing species, whereas a single species subject to the same environmental variability may track the resource maximum closely and maintain a much more stable population size. Other studies have shown that competitive interactions may amplify changes in mean population sizes due to environmental changes and thereby increase extinction risks. This study accentuates the harmful role of competitive interactions by illustrating that they may also decrease rates of adaptation. The slowdown in evolutionary rates caused by competition may also contribute to explain low rates of morphological change in spite of large environmental fluctuations found in fossil records. 相似文献
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